--- a/autoconf/ast_ext_tool_check.m4
+++ b/autoconf/ast_ext_tool_check.m4
@@ -8,13 +8,16 @@ AC_DEFUN([AST_EXT_TOOL_CHECK],
 	AC_REQUIRE([AST_PROG_SED])dnl
 	if test "x${PBX_$1}" != "x1" -a "${USE_$1}" != "no"; then
 		PBX_$1=0
-		AC_PATH_TOOL(CONFIG_$1, $2, No, [${$1_DIR}/bin:$PATH])
+		if test "x${$1_DIR}" != "x"; then
+			AC_PATH_TOOL(CONFIG_$1, $2, No, [${$1_DIR}/bin:$PATH])
+		else
+			AC_PATH_TOOL(CONFIG_$1, $2, No, [$PATH])
+		fi
 		if test ! "x${CONFIG_$1}" = xNo; then
 			$1_INCLUDE=$(${CONFIG_$1} m4_default([$3],[--cflags]))
-			$1_INCLUDE=$(echo ${$1_INCLUDE} | $SED -e "s|-I|-I${$1_DIR}|g" -e "s|-std=c99||g")
+			$1_INCLUDE=$(echo ${$1_INCLUDE} | $SED -e "s|-std=c99||g")
 
 			$1_LIB=$(${CONFIG_$1} m4_default([$4],[--libs]))
-			$1_LIB=$(echo ${$1_LIB} | $SED -e "s|-L|-L${$1_DIR}|g")
 
 			m4_ifval([$5], [
 				saved_cppflags="${CPPFLAGS}"
